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    <script>
        // 1. 求数组 [2, 6, 1, 7, 4] 里面所有元素的和以及平均值。
        let arr = [2, 6, 1, 7, 4];
        let sum = 0;
        for (let i = 0; i < arr.length; i++) {
            // console.log(arr[i]);
            sum = sum + arr[i];
        }

        console.log('数组的和是' + sum);
        console.log('数组的平均数是' + sum / arr.length);
    </script>
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